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topic 43248

Two-step black color anodizing w/tin sulfate

A discussion started in 1998 but continuing through 2020


Q. DC/AC equipment for colour anodizing? I am looking for information on how to specify ripple, control, get the best choice for electro coloring anodizing in tin sulfate solutions.

Thank you, very much.

Gustavo C. Giraudo


A. I think such specifications are confidential information of manufacturers of AC/DC equipment who have spent a lot of money to develop them..

The best way to have such equipment is to contact with the AC/DC power suppliers' manufacturers and buy a suitable one.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey


A. I slightly and respectfully disagree with Mr. Ulucak just a bit, because there are some people who feel that complicated and expensive proprietary waveforms are a waste of money in tin-based electrocoloring, and that all that is required is low voltage AC. So I think that the starting point is to hear that side of the issue before listening to sales pitches about the benefits of special waveforms.

"Electrolytic Coloring of Anodized Aluminum Using Tin Electrolytes" by Gohausen & Schoener (Plating & Surface Finishing, Feb. 84) is a great intro to the topic. Best of luck.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha


Q. I was reading your response above and I'm interested in know more about electro coloring anodizing, at this time I'm coloring with Tin solution, but I have doubts about output voltages, I have an 3000 amp 30 volts AC coloring power supply by Dynapower, with five steps:

1.-dwell time
3.-stage # 1
4.-stage # 2

Where can I get "Electrolytic Coloring of Anodized Aluminum Using Tin Electrolytes" by Gohausen & Schoener (Plating & Surface Finishing, Feb. 84) ?

Or a newest ?

Marco Lopez
- Guadalajara, Jalisco, Mexico


A. You may be able to get a copy from the publisher of Plating & Surface Finishing, the A.E.S.F. Contact their publications department at

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)


Q. Could Tin sulfate be used for coloring (black) aluminum utensils (AA3003 alloy) in hard anodizing process? If yes, is it harmful for health.

Yasar Bayraktar
- Seydisehir, Konya, Turkey


A. Salam:
tin sulfate is a green chemical, not harmful. But blackening with that is not an easy technique.
It's better to trial first according to additional chemical, concentration, timing and current density used.

harmanto soebawi
- bangka island, indonesia


Q. I purchase an anodizing service loosely described as "two step" in my specifications, which also refer to tin sulfate in the process. The anodizer who currently provides this service tells me that the tin sulfate is the second step and provides the black finish my parts have after processing (the first step is merely a clear anodize). I am not familiar with this process and would like to know if a)it is commonly known by another name, b)if it's a relatively common process that can be found globally (my primary machining supplier is in Singapore and I would like to see if he can provide parts complete) and c)if the minimum lot charge of nearly double what I pay for my other anodizing jobs is justified. Thanks in advance for any assistance that might be provided.

Fred Tafel
- Mentor, Ohio, USA

affil. link
"Surface Treatment & Finishing of Aluminium and Its Alloys"
by Wernick, Pinner & Sheasby
from Abe Books
info on Amazon

affil. link
probert book
Aluminum How-To

"The Chromating - Anodizing - Hardcoating Handbook"
by Robert Probert


A. Anodizing without subsequent dying produces "clear" aluminum colored parts, Fred, assuming the aluminum is quite pure. If the alloy is rich in copper or silicon, even clear anodizing will come out gray to charcoal.

Anodized parts can be dyed with organic dyes (rather similar to clothes dye but optimized for aluminum), but such colors are not completely lightfast . . . sometimes not very lightfast at all. For greater lightfastness, metal salts are electrolytically deposited at the base of the anodizing pores, and this is called two-step anodizing. And yes, every anodizing shop should have at least a general understanding of the concept even though most probably don't offer it themselves.

Two-step anodizing involves this second electrolytic process and it may also involve a subsequent organic dye to get a fully saturated color as well. It is a premium process, and not all shops are set up to be able to do it, so it will be more expensive. It's hard to say from a distance whether "nearly double" is the right price, but it doesn't seem to be the manifestly wrong price.

Anodizers apply their decades of experience to get you a good finish, so don't make the mistake of thinking anybody can do it, and easily. That is not to assert that there are no shops in and around Singapore with the requisite experience, but it is to say that you shouldn't let a shop "try their hand" at it. You need to find a shop which already does two-step anodizing and you need to have sample parts that they produced in hand before making commitments. Good luck.

Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)

February 24, 2011

Q. We are designing a new production line to produce mirror image of nickel finish for aluminium profile . So far I have been unable to find out the chemical that needed for nickel finish and the way of doing it. We able to produce the mirror image by using three chemicals which are H3PO4, H2SO4 and HNO3. But we have difficulty in getting the nickel finish color (some sort like light champagne color). Seeking for expertise here.
Thanks in advance.

Jay Lee
process engineer - Klang, Selangor, Malaysia

February 25, 2011

A. Hi, Jay.

There should be plating and anodizing process suppliers or consultants in your area who can help you get started; you do not need to independently re-invent these technologies. It sounds like you are doing brite-dipping of aluminum. To my knowledge this process will not by itself produce any coloration. After that, I think you will need to anodize the sheet, dye it with a nickel or light champagne dye, and then seal it.


Ted Mooney, Teds signature
Ted Mooney, P.E. - Pine Beach, New Jersey
Striving to live Aloha

February 25, 2011

Q. I agree with you that brite-dipping of aluminum will not produce any coloration. Our lines do have anodizing process. But I do not have any ideas on how to produce the nickel finish after anodizing process (We have no problem on the anodizing process).
What is the chemical solution that needed (nickel sulphate)? What is the concentration and the process parameter (eg. temperature, pH...). Is this process called nickel plating? Hope that someone can give me a hand on this.

Jay Lee [returning]
- Klang, Selangor, Malaysia

simultaneous February 28, 2011

Jay, if you are looking to give a champagne color (similar to ENP shade)to the anodized aluminum, you would have to electro color the articles in a tin sulphate solution for a few seconds. You would have to add the electro color bath to your anodizing line for this purpose.Please understand that the bath has to be regularly maintained to give consistent color. Color can also vary depending on the aluminum alloys.

Winston D'Souza
- Bombay, India

February 28, 2011


Your second posting make things a lot clearer.The process you are looking for is not nickel plating. It is called electrolytic coloring, usually for architectural profiles. The beauty electrolytic coloring is that they don't fade when expose to to UV light ( sunlight ) as compared to organic dyes.

Electrolytic coloring deposits metal salts into the anodized pores, usually, salts of nickel,cobalt, tin etc., using AC voltage. Yes, nickel sulfate is one of the metal salts used. Instead of re-inventing the wheel, you'll be better off getting the coloring solutions from suppliers which comes along with tech support.

SK Cheah
- Penang, Malaysia

Tin sulphate concentration in electrolytic coloring bath jumps up & down

June 16, 2017

Q. Dear finishing team ,
I am a laboratory technical in aluminum extrusion company
I want to ask about coloring bath , it must be (17-19)g/l concentrated of SnSO4 ,and we reach this level of concentration but suddenly it dropped down to 13 and can't make it rise to 17 anymore , we added a lot of gallons to repair it but it still 13-14 g/l
after two months it repair it self and give us 17-19 g/l concentration without we do any thing to it !
Now a days we have this problem again , the concentration dropped to 14 g/l, we added 10 gallons which is 25kg for each gallon then the concentration rise to 16
next day we add 6 gallons and it still 16 ! we added another 6 gallons in the next day and it still 16 !
I hope to find justification for this and what should we do !
Best regards,

Eng. abeer abuzaid
engineer - Amman, Jordan

Why does electrolytic coloring use AC current?

June 19, 2017

Q. I have a question about electrolytic coloring on anodized aluminium. Why this process use AC to deposit color? In my understand I think this technique like a electrolytic deposition technique that use DC to do. And I would like to tell you that I very new in this field especially about electric so I would like to apologize you if my question is like a stupid question. And the second is if I do some experiment what is the criteria to choose AC or DC to do? Because I'm very confuse about that like a electrolytic coloring technique that I mention above.

Thank you everyone to suggest me ^^.

Nattapon Pornnumpa
- Bangkok. Thailand

Chalking after electrocolor dying process on anodized aluminum

August 28, 2019

Q. Good am sirs,
we have a problem about our aluminum finished product, the surface becomes powdery after our electrocoloring process and it has an effect on the color appearance of the aluminum, I hope you can help me -- we are using a tin bath and the temp. of the solution ranges from 20-25 °C, std stannous concentration is 5-15 g/L actual: 7g/L
Nickel Sulphate: 26 g/L

Thank you in advance!

dhazel de mesa
- philippines

December 24, 2019

Q. Hello.
What is your opinion for black colour for anodizing aluminum in the electrocolouring bath?

What is the advantage and disadvantage?

mary alaii
aldoran - mosel.iraq

Bleed out problem with black anodize on a tin sulfate electro color process

March 19, 2020

Q. Hi! I'm a chemical engineer in charge of an anodizing plant of aluminum profiles for architectural purposes (6061).
We are having an issue with our darker finishings like dark bronze and black. The color "bleed out" after the cold sealing. We tested removing one profile of the rack before the submersion in the sealing bath. The difference is overwhelming.


We decided to change the sealing bath, cause we knew it was contaminated with Al, but after that there were no improvements.
After an analysis we can not ensure if the problem is the sealing or a bad deposition of tin into the pores.
Process info:
Anodize: 150g/L sulphuric, 20-21 °C, <10 g/L Al, 15 microns.
Electrocolor: 9,5 g/L tin sulfate product, 20 g/L sulphuric.
Sealing: Nickel base product.

I hope someone had dealt with some similar problem.

Enzo F. Castro
- Corrientes, Argentina

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